In general, cryogenic devices fall within one of two categories, namely, those utilizing high pressure gas to produce low temperatures by the Joules-Thompson phenomena and the second utilizing liquid cryogen which vaporizes extremely rapidly at room temperature and pressure. Joules-Thompson equipment typically utilizes gas stored at 500 to 800 psi which is expanded to atmospheric pressure in close proximity to tissue to be necrotized. Such equipment requires adequate safeguards to protect the patient and operator against the hazards associated with these high pressures. Cryogenic devices using liquid cryogen typically operate at relatively low pressures of about 1 atmosphere and can apply a spray of finely divided liquid cryogen directly to the surface to be necrotized, or to the interior of a probe, in each instance utilizing the latent heat of evaporation in a highly effective and efficient manner. Spray devices using liquid cryogen are much faster, particularly when freezing tissue to depths in excess of one or two millimeters. An adequate supply of cryogen can be stored in a small heat insulated container readily held and manipulated in the operator's hand.
Various devices designed for liquid cryogen heretofore proposed are subject to numerous disadvantages avoided by this invention. Typical U.S. Pat. Nos. disclosing liquid cryogenic devices include Nelson 1,659,663; Posch 2,645,097; Johnston 3,220,414; Leigh 3,298,371; Bryne 3,534,739, 3,651,813, 3,712,306; Zacarian 3,702,114; Reynolds 3,739,956; Kollner 3,794,039; Tromovich 3,823,718. No one of these devices can selectively dispense single or a two phase jet of cryogen at the user's option. Single phase and two phase jets have distinctly different cooling capacities and fields of usefulness. A cryogenic device providing the selective choice of single or two phase jets is disclosed in my co-pending application for United States Letters Patent, Ser. No. 936,909, filed Aug. 25th, 1978, now abandoned. That device is instantly convertible between single and dual phase operation by manipulation of a single control means when equipped with any one of a limited range of relatively small diameter dispensing nozzles, that is, nozzles having a diameter of v=0.015 inches, approximately, or less.